Seasonal rainfall during southwest monsoon mostly hangs around ‘Below Normal’, ‘Normal’ and ‘Above Normal’. The other 2 categories of ‘Drought’ and ‘Excess’ get outnumbered by large margins. ‘Drought’ or Deficient’ monsoon is announced when the seasonal rainfall drops below 90% of long period average (LPA). Similarly, ‘Excess’ monsoon is declared when the rainfall climbs to > 110% of LPA.
Since 1950,there have been 8 ‘Excess’ seasons and the most rainiest of these was 1961 with a surplus of 21.8%. The 2nd best being 1988 with a seasonal mark of 119.3% of LPA. From 1950 onward, there was always >/= 1 excess season in each decade. However, since the year 2000, not even a single season has recorded excess rainfall.
Long Period Average of southwest monsoon season is gradually lowering, except for one odd year in between. Between 2005 and 2022, the seasonal LPA has dropped from 892.5mm to 868.6mm. Till last year (2021), this seasonal figure was 880.6mm and a straight fall of 12mm to 868.6mm in 2022.
Ideally, the rainfall need to be updated after one decade. The current LPA of 868.6mm is calculated with data base 1971-2020. The decadal rainfall was also noticed dipping till the last decade(2001-2010). LPA for the decade 1981-1990 was 881mm which dipped to 847mm for 2001-2010. Courtesy, 2 above normal monsoon in 2019 & 2020, the decadal average for 2011-2020 climbed to 861.7mm. Apparently, southwest monsoon has ‘good’ and ‘poor’ cycles which last for 10-20 years. There was no drought between 1921-1940. Again, there was no drought for 14 years, from 1988 to 2001. However, 5 droughts were witnessed between 2002 and 2015. Presumably, the monsoon has entered a ‘good’ cycle since 2019. It has scored a hat trick of above normal/ normal monsoon between 2019-2021. This score is expected to extend in to the current season and is likely to end on a positive note.